Japanese Patent Kokai No. 11,090/2001 disclosed that D-psicose can be advantageously used as a low-calorie sweetener for producing low-calorie foods and beverages. In addition, Japanese Patent Kokai No. 213,227/2005 disclosed that D-psicose can be advantageously used for health foods, foods and beverages for diabetic patients, and foods and beverages for sliming.
Ken Izumori et al., Biosci. Biotech. Biochem., 57, 1037-1039 (1993) disclosed a D-ketohexose 3-epimerase from Pseudomonas cichorii ST-24 and that D-psicose can be produced from D-fructose by using the enzyme. However, the enzyme is sometimes referred to as “D-tagatose 3-epimerase” and is known to be an enzyme most specific to D-tagatose and having a relatively low activity on D- fructose. Further, Pseudomonas cichorii is not preferable to use for industrial production because the bacterium is a phytopathogenic microorganism and its ability to produce the D-ketohexose 3-epimerase is very low. Under the circumstances, a microorganism with a high ability to produce a ketose 3-epimerase, except for the genus Pseudomonas, and a ketose 3-epimerase with a high specificity D- fructose, being preferable for the production of D-psicose, are desired.